What they need is a consistantly growing PS Plus install base for the first year. 12/100 people on my friends list have thus far subscribed to the service, but almost all of those subscribed in the first month, with maybe one subscribing since. This results in a very profitable first month, and a very profitable month when all those people have to renew, but that isn't until October of next year given the three free months for signing up over the first two months. So that's two months in over a year in which they'll make a decent return on the service.
They need a steady stream of new people signing up over that first 12 months for a consistant profit base, one that continues each consecutive year with renewals.
The only things appearing soon that could convince more people to sign up are the LBP2 and KZ3 betas, which I assume will be PS Plus exclusive for at least some time.
